1. Field of the Invention
The present invention relates to a system for estimating a rolling condition of a vehicle such as an automobile.
2. Description of the Prior Art
When a vehicle such as an automobile is driven to turn along a curved course, its body flexibly supported above its wheels via elastic suspensions inclines outside of the turn according to a centrifugal force acting virtually at the center of gravity of the vehicle body.
A parameter which indicates how far the vehicle body is proceeding in such a rolling movement is useful for automatic behavior controls of vehicles such as an automatic suspension control for automatically varying the spring constant and/or the damping coefficient of the suspensions, a vehicle stability control for automatically braking a selected one or more of pairs of front and rear wheels so as particularly to stabilize the turning performance of the vehicles. It would also be desirable for a driver of a vehicle if the vehicle is equipped with an indicator for indicating to the driver when such a rolling of the vehicle body due to the turning centrifugal force is imminent.
In Japanese Patent Laid-open Publication 6-297985, it has been proposed to estimate the roll angle of a body of a four wheeled vehicle based upon three displacement sensors provided to detect a displacement of each of three wheels selected from the four wheels relative to the vehicle body and a lateral acceleration sensor, such that a three dimensional position of a virtual plane traversing three fixed points of the vehicle body relative to the ground surface is calculated based upon the output of the three displacement sensors by solving three one-dimensional three variables simultaneous equations so as thereby to determine the height of the center of gravity of the vehicle body above the ground surface, and a torque for rolling the vehicle body is calculated by multiplying the height with the mass of the vehicle body and an output of the lateral acceleration sensor. According to the invention described in this publication, the vehicle is automatically braked when the roll angle exceeds a predetermined threshold value.
In Japanese Patent Laid-open Publication 63-116918, it has been proposed to estimate a rolling condition of a vehicle based upon load sensors for detecting loads of actuators provided for respective wheels, a vehicle speed sensor, a steering angle sensor, displacement sensors and an acceleration sensor. According to the invention described in this publication, the estimated rolling condition is shown to the driver by an indicator, and when the rolling condition exceeds an allowable limit, the vehicle is automatically braked, with execution of an engine slow down.
In Japanese Patent Laid-open Publication 3-70614, it has been proposed to estimate roll angle of a vehicle body by assuming a vehicle as a simple harmonic rotary oscillation system, such that the roll angle of the vehicle body is obtained as a solution for the rotational angle of the simple harmonic rotary oscillation equation based upon displacements of the vehicle body detected at front left, rear left, front right and rear right wheels and a lateral acceleration detected by a lateral acceleration sensor. According to the invention of this publication, the roll angle thus estimated is supplied to a control unit for controlling active suspensions of the four wheels, together with other input parameters such as vehicle speed, pitch angle of the vehicle body, pressure of a main tank of the control system, etc.
The present application contemplates that in evaluating the rolling of a vehicle body caused by a turn running thereof, it will be worthwhile to estimate it as a xe2x80x9crolling conditionxe2x80x9d indicative of how close the rolling is momentarily approaching to a limit thereof allowable for ensuring a stabilized running of the vehicle.
In is therefore a primary object of the present invention to provide a device for estimating such a xe2x80x9crolling conditionxe2x80x9d of the vehicle body that is indicative of how close the rolling is momentarily approaching to an allowable limit thereof so as to ensure a stabilized running of the vehicle, wherein the rolling condition is not a mere roll angle of the vehicle body but a quantity which is informative of the current rolling state in reflection of its allowable limit and in connection with an urgency of counteracting thereagainst.
In order to accomplish such a primary object, the inventor proposes a device for estimating a rolling condition of a body of a vehicle having the vehicle body, a pair of front wheels, a pair of rear wheels, and suspension means for supporting the vehicle body on the pairs of front and rear wheels, the vehicle body being able to roll relative to the wheels around a virtual axis of rolling provided by the suspension means, the device comprising:
means for estimating a first quantity corresponding to roll angle of the vehicle body around the rolling axis;
means for estimating a second quantity corresponding to a change rate of the roll angle of the vehicle body;
means for estimating a third quantity indicating a relative magnitude of the first quantity with reference to a first limit value predetermined therefor;
means for estimating a fourth quantity indicating a relative magnitude of the second quantity with reference to a second limit value predetermined therefor; and
means for estimating the rolling condition as a combination of the third and fourth quantities such that the rolling condition is intensified along with increase of the third quantity as well as increase of the fourth quantity.
The above-mentioned device according to the present invention, when it comprises at least one selected from the group consisting of means for detecting lateral acceleration Gy of the vehicle body, a combination of means for detecting yaw rate xcex3 of the vehicle body and means for detecting vehicle speed V, and a combination of means for detecting yaw rate xcex3 of the vehicle body and means for detecting lateral acceleration Gy, may be constructed such that the second quantity estimation means comprise means for cyclically conducting such calculations as
{dot over (xcfx86)}(t+xcex94t)={dot over (xcfx86)}(t)+{xcfx89o2(xcex3Vxcfx86oxe2x88x92xcfx86(t))xe2x88x922xcfx89oxcex6{dot over (xcfx86)}(t)}xcex94t and
xcfx86(t+xcex94t)=xcfx86(t)+{dot over (xcfx86)}xcex94t
at a minute cycle time xcex94t of time t so as to cyclically renew values of {dot over (xcfx86)} and xcfx86 by respective newly calculated values thereof and to estimate the third quantity by dividing each instant value of {dot over (xcfx86)} by a limit value {dot over (xcfx86)}limit predetermined therefor as an allowable limit thereof, wherein xcfx86 is the roll angle of the vehicle body around the rolling axis, {dot over (xcfx86)} is change rate of the roll angle xcfx86, xcfx89o is a natural frequency of the vehicle body in rolling around the rolling axis in oscillation, X is either the lateral acceleration Gy, xcex3V or Ff representing (I{dot over (xcex3)}+LrMGy)/H, xcfx86ois a roll angle induced in the vehicle body by a unit lateral acceleration applied thereto, and xcex6 is a damping coefficient in the rolling of the vehicle body around the rolling axis, while I, Lr, M and H are the inertial moment of the vehicle body in yawing around the center of gravity thereof, a distance between the axis of the rear wheels and the center of gravity of the vehicle body, the mass of the vehicle body, and the wheel base of the vehicle, respectively.
According to the optional provision of the means for detecting the yaw rate xcex3, the means for detecting the vehicle speed V, and/or the means for detecting the lateral acceleration Gy, the means for estimating the third quantity may estimate the third quantity as either xcex3V/(xcex3V)limit by dividing each instant value of a product of xcex3 and V by a limit value (xcex3V)limit predetermined therefor as an allowable limit thereof, Gy/Gylimit by dividing each instant value of Gy by a limit value Gylimit predetermined therefor as an allowable limit thereof, Ff/Fflimit by dividing each instant value of Fy by a limit value Fflimit predetermined therefor as an allowable limit thereof, or a weighted combination of xcex3V/(xcex3V)limit, Gy/Gylimit, and Ff/Fflimit according to the running conditions and/or road conditions.
The means for estimating the third quantity may also estimate the third quantity as xcfx86/xcfx86 limit by dividing each instant value of xcfx86 in the cyclical calculation by a limit value xcfx86limit predetermined therefor as an allowable limit thereof.